Method of reducing semiconductor window layer loss during thin film photovoltaic device fabrication, and resulting device structure

ABSTRACT

A completed photovoltaic device and method forming it are described in which fluxing of a window layer into an absorber layer is mitigated by the presence of a sacrificial fluxing layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/789,650, filed on Mar. 15, 2013, which is hereby fully incorporatedby reference.

BACKGROUND OF THE INVENTION

Photovoltaic (PV) devices are PV cells or PV modules containing aplurality of PV cells or any device that converts photo-radiation orlight into electricity. Generally, a thin film PV device includes twoconductive electrodes sandwiching a series of semiconductor layers. Thesemiconductor layers include an n-type window layer in close proximityto a p-type absorber layer to form a p-n junction. During operation,light passes through the window layer, and is absorbed by the absorberlayer. The absorber layer produces photo-generated electron-hole pairs,the movement of which, promoted by an electric field generated at thep-n junction, produces electric current that can be output through thetwo electrodes.

Since light has to pass through the window layer to be converted toelectricity, it is desirable to have a thin window layer that allows themost amount of light to pass therethrough. The more light that passesthrough the window layer, the more efficient the device. Thus, onemethod that has been used to increase device photo-conversion efficiencyis to use a window layer that is as thin as possible, while maintainingthe p-n junction with the absorber layer.

Another method that has been used to enhance device photo-conversionefficiency is to subject the absorber layer to a cadmium chloride(CdCl₂) activation treatment. Alternative compounds for the activationtreatment can also be used such as, for example, NHCl₂, ZnCl₂, TeCl₂, orother halide salts.

The CdCl₂ activation treatment increases the grain size and reducesdefect areas in the absorber layer. Specifically, one factor that maylimit thin-film photo-conversion efficiency is the number ofphoto-generated electron-hole pairs (i.e., carriers) that are trappedand then recombined before they are output as electricity by the device.In some instances, carriers may get trapped at structural defects suchas defective grain boundaries within various layers of the device. Forexample, the semiconductor absorber layer is formed of grains, alsoknown as crystallites. Crystallites are small, microscopic crystals,where the orientation of the crystal lattice within the crystallite isthe same. But, a defect exists where the orientation of the crystallattice changes from one grain to another. Hence, the crystallites thatmake up the absorber layer may be said to have defective grainboundaries where crystallites on each side of the boundary areidentical, except in crystal orientation.

In any case, the larger the grains that make up the absorber layer, thelesser the number of grain boundaries present in the absorber layer.Thus, the CdCl₂ activation treatment increases the size of the grains orcrystals that make up the absorber layer and thus reduces the number ofgrain boundaries available to trap carriers. Device efficiency may thusbe enhanced.

For example, a thin-film PV device may have a window layer formed ofcadmium sulfide (CdS) and an absorber layer formed of cadmium telluride(CdTe). The CdCl₂ activation treatment includes applying CdCl₂, forexample, in liquid or vapor form, to the CdTe of the absorber layer, andthen annealing the absorber layer at a particular anneal temperature,for example about 400° C. to about 420° C., for a particular annealtime, for example, from about 10 minutes to about one hour. The annealtemperature is generally high enough and the anneal time long enough topromote recrystallization of the CdTe crystallites.

The recrystallization of the cadmium telluride can take two forms or acombination of the following two forms: (1) intragrain or primaryrecrystallization (recrystallization that changes crystallite grainorientation); and (2) intergrain or secondary recrystallization(recrystallization resulting from grain coalescence).

The primary crystallization leads to adjacent grains, which wereoriented differently, to now be oriented in the same direction. Hence,primary crystallization results in a lesser number of defectiveboundaries being available to trap carriers therein. By contrast, thesecondary recrystallization results in grain growth as smaller grainscoalesce into larger ones. Thus, it too, leads to a reduced number ofgrain boundaries, which could contain defects.

Further, in addition to reducing the number of defective grainboundaries in the absorber layer, the CdCl₂ activation treatment alsorepairs some of the defects in the grain boundaries. This is donethrough the incorporation of chlorine atoms (or ions) from the CdCl₂into the CdTe absorber layer. Other mechanisms believed to repair orpassivate such defects include the formation of doping complexes withinthe absorber layer created by cadmium vacancies, the incorporation ofchlorine atoms to occupy tellurium sites, and inter-diffusion ofmaterials between the absorber layer and the semiconductor window layer.

The CdCl₂ and the heat from the CdCl₂ activation treatment, while beingbeneficial in reducing the number of defective grain boundaries in theabsorber layer may also promote chemical fluxing. Fluxing occurs when achemical element from one layer of a photovoltaic device underfabrication, where it is in high concentration, flows into another layerwhere there is a low concentration, or where it is not.

In this case, the CdCl₂ activation treatment may increase the mobilityof sulfur atoms from a CdS window layer causing it to diffuse into aCdTe absorber layer. This fluxing of sulfur can consume the CdS in thewindow layer, overly thinning the layer and, in extreme situations,entirely removing it in some areas resulting in areas where the p-njunction is degraded or lost. The total removal of the CdS window layermay be exacerbated in devices where a very thin window layer wasinitially used to enhance device efficiency.

It would be desirable, therefore, to provide a technique for reducing orcontrolling the amount of sulfur fluxing from the window layer into theabsorber layer during a CdCl₂ activation treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of an intermediate photovoltaic device inaccordance with a disclosed embodiment;

FIGS. 2A and 2B show a side view of a photovoltaic device at variousstages of manufacture in accordance with a disclosed embodiment;

FIGS. 3A and 3B show a scanning electron microscope image of a side viewof an example intermediate photovoltaic device and an intermediatephotovoltaic device in accordance with a disclosed embodiment; and

FIG. 4 shows a side view of a photovoltaic device in accordance with adisclosed embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein provide a method of forming PV deviceshaving a sulfur containing window layer, e.g. CdS, and an absorberlayer, e.g. CdTe. The method includes forming an additional layercontaining sulfur near or within an absorber layer of the device. Thesulfur in the additional layer is used to minimize or control fluxing ofsulfur from the window layer to the absorber layer during a CdCl₂activation treatment. This will allow a sufficient p-n junction to bemaintained in the completed PV devices. Since the additional layer isused for the sole purpose of providing sulfur to the absorber layerduring a CdCl₂ activation treatment and since it may be consumedentirely during such treatments without any ill effect to the devices,it will henceforth be referred to as a sacrificial layer.

For illustrative purposes, embodiments are described below withreference to a thin film PV device, which may include a PV cell, acollection of cells forming a module, or any portion or combinationthereof. However, it should be understood that the embodiments may applyto devices other than thin film devices.

Now referring to the accompanying figures, wherein like referencenumbers denote like features, FIG. 1 illustrates an exemplary PV device100 undergoing fabrication. The PV device 100 includes a transparentsubstrate 102 upon which a transparent conductive oxide (TCO) stack 114,a semiconductor window layer 116, a first absorber layer 120 a, asacrificial layer 118 and a second absorber layer 120 b may respectivelybe formed.

The substrate 102 is used to protect the PV device 100 fromenvironmental hazards. Since the substrate 102 receives light incidenton the PV device 100, it should be made of a transparent material. Inthis case glass or any other suitable material may be used, such asborosilicate glass, soda lime glass, float glass, or polymer.

TCO stack 114 includes an optional barrier layer 108, TCO layer 110, andan optional buffer layer 112. The TCO stack 114 may be pre-formed onsubstrate 102 and the pre-formed TCO stack 114 on substrate 102 may bepurchased from a commercial supplier. Alternatively, the TCO stack 114may be formed one layer at a time over substrate 102 during fabricationof device 100. In any case, the barrier layer 108 is used to inhibitsodium diffusion from the substrate 102 into other layers (i.e., thewindow and absorber layers) of the device. Sodium diffusion into theselayers may adversely affect device efficiency. The barrier layer 108 canbe a bi-layer of an SnO₂ layer 104 over the substrate 102 and an SiO₂layer 106 over the SnO₂ layer 104 or a single layer of SiO₂ or SnO₂.

The TCO layer 110 functions as one of the two output electrodes of thedevice. Since light has to pass through the TCO layer 110 to reach thesemiconductor layers where it is converted to electricity, it may bemade of a transparent conductive material such as indium tin oxide(ITO), fluorine doped tin oxide (SnO₂:F), or cadmium stannate (Cd₂SnO₄).

The buffer layer 112, may be used to provide a smooth layer upon whichthe window layer 116 may be deposited. The smoother the layer upon whichthe window layer 116 is deposited, the thinner the window layer 116 maybe without compromising the p-n junction. The buffer layer 112 may bemade of a metal oxide such as SnO₂, ZnO, or a combination of ZnO andSnO₂.

Over the TCO stack 114, a semiconductor multi-layer 122 is provided thatincludes an n-type window layer 116, a p-type absorber layer 120 a, asacrificial layer 118 and a second p-type absorber layer 120 b. Thoselayers are described in more detail below.

The semiconductor window layer 116 of thickness 116 t is formed adjacentto TCO stack 114. Semiconductor window layer 116 is preferably formed ofcadmium sulfide. However, it should be understood that other n-typesemiconductors may be used including, but not limited, to cadmium zincsulfide. Window layer thickness 116 t may be greater than about 50 Å.Generally, the window layer thickness 116 t can be between about 50 Åand about 2000 Å, between about 100 Å and about 2000 Å, between about 75Å and about 1000 Å, or greater than 0 Å and less than about 200 Å.

The first semiconductor absorber layer 120 a of thickness 120 at isformed adjacent to semiconductor window layer 116. First absorber layer120 a is a p-type semiconductor that may be made of cadmium telluride.However it should be understood that other p-type semiconductors may beused. First absorber layer thickness 120 at may be greater than about 10Å. For example, the thickness of the first absorber layer 120 a may bebetween about 10 Å and about 50,000 Å, between about 10,000 Å and about50,000 Å, between about 10,000 Å and about 30,000 Å, or between about15,000 Å and about 25,000 Å.

The sacrificial layer 118 of thickness 118 t is formed adjacent to firstabsorber layer 120 a. Sacrificial layer 118 preferably includes the samematerial as semiconductor window layer 403, as discussed further below.Thus, in the present embodiment, sacrificial layer may be made ofcadmium sulfide or cadmium zinc sulfide. Sacrificial layer thickness 118t may be greater than about 50 Å. Specifically, it may be between about50 Å and about 1000 Å, between about 100 Å and about 1000 Å, betweenabout 100 Å and about 800 Å, or between about 400 Å and about 600 Å.

The second semiconductor absorber layer 120 b of thickness 120 bt isformed adjacent to sacrificial layer 118. Second absorber layer 120 b isa p-type semiconductor of the same material as first absorber layer 120a (e.g., cadmium telluride). However, it should be understood that otherp-type semiconductors may be used, including materials different thanfirst absorber layer 120 a materials. Second absorber layer thickness120 bt may be greater than about 500 Å. That is, the thickness of thesecond absorber layer 120 b may be between about 500 Å and about 50,000Å, between about 10,000 Å and about 50,000 Å, between about 10,000 Å andabout 40,000 Å, or between about 20,000 Å and about 30,000 Å.

The layers of the PV device 100 may be formed using any known depositiontechnique or combination of techniques. For example, the layers can beformed by chemical vapor deposition (CVD), physical vapor deposition(PVD), chemical bath deposition (CBD), low pressure chemical vapordeposition, atmospheric pressure chemical vapor deposition,plasma-enhanced chemical vapor deposition, thermal chemical vapordeposition, DC or AC sputtering, spin-on deposition, spray-pyrolysis,vapor transport deposition (VTD), closed space sublimation (CSS), assome examples, or a combination thereof. These processes are well knownin the industry and thus will not herein be described in detail.

Referring to FIGS. 2A and 2B, after the second absorber layer 120 b isdeposited, a CdCl₂ 200 activation treatment may ensue. As noted earlier,during the CdCl₂ activation treatment, the chlorine compound and theassociated heat treatment increase sulfur mobility in the window layer116 and, in the case of the present embodiment, in the sacrificial layer118 as well, causing the sulfur to be more easily fluxed, e.g. dissolvedinto absorber layers 120 a and 120 b.

As noted above, if the sacrificial layer 118 is not used, then duringthe CdCl₂ activation treatment the sulfur in the semiconductor windowlayer 116 could dissolve into the adjacent absorber layer 120 untileither the sulfur solubility limit of the absorber layer 120 is reached,there is no more sulfur left in the window layer 116, or the activationtreatment is concluded. The sulfur solubility limit refers to themaximum amount of sulfur that can be dissolved into the absorber layer120 for a given activation treatment condition. If the sulfur solubilitylimit of the absorber layer is reached before the CdS of the windowlayer 116 is degraded, there may remain a p-n junction between thewindow layer and the absorber layer. But, if the sulfur solubility limitof the absorber layer is not reached before the CdS of the window layer116 is consumed, then the window layer or portions of the window layermay disappear altogether, eliminating or severely degrading the p-njunction.

By providing the sacrificial layer 118 between the first and the secondabsorber layers 120 a, 120 b, sulfur from the window layer 116 may notbe used, and if used, may be used in a lesser or controlled amount thanif the sacrificial layer 118 was not present in the device during theCdCl₂ activation treatment. As a result, it is possible to use moreaggressive CdCl₂ activation treatment conditions (e.g., higher chlorineconcentration, higher annealing temperature, and/or for a longer periodof time) without compromising the p-n junction of the device 100.Because PV device 100 may be subjected to more aggressive CdCl₂activation treatment conditions, grain boundaries and defects within theabsorber layers 120 a, 120 b may be further reduced as compared to PVdevices, where the absorber layer is subjected to less aggressive CdCl₂activation treatment conditions.

During the CdCl₂ activation treatment, the sacrificial layer 118 maydissolve into absorber layers 120 a, 120 b at a higher rate than thesemiconductor window layer 116. This is due to: (1) the closer proximityof sacrificial layer 118 to the layer upon which the chlorine compoundis applied, and (2) the sacrificial layer 118 being between the twoabsorber layers allowing its sulfur to diffuse from both its upper andlower surfaces into the adjoining absorber layers 120 a, 120 b. Becausethe sulfur in the sacrificial layer 118 is dissolved at a higher ratethan that of the semiconductor window layer 116, the sulfur solubilitylimit of the absorber layers 120 a, 120 b is more quickly approachedreducing the amount of sulfur that is fluxed from the semiconductorwindow layer 116 into the absorber layers 120 a, 120 b and allowing forthe p-n junction to be maintained between the window layer 116 and theabsorber layer 120.

Note that choosing the same material for sacrificial layer 118 as thatof the semiconductor window layer 116 is preferable. This is because thesulfur solubility limit of the absorber layers 120 a, 120 b may bereached more quickly using the same material for both the window layer116 and the sacrificial layer 118 than with using different materials.Nonetheless, the sacrificial layer 118 need not be of the same materialas that of the window layer 116. The sacrificial layer 118 may be madeof other materials that reduce sulfur fluxing in the window layer 116during the CdCl₂ activation treatment of the absorber layers 120 a, 120b.

Another advantage of providing sacrificial layer 118 in association withthe absorber layers 120 a, 120 b is that the sulfur in the sacrificiallayer 118 can also serve to improve the physical and electricalcharacteristics of the absorber layers 120 a, 120 b surface and graindefects in much the same way as Cl atoms from the CdCl₂ activationtreatment improve the absorber layers 120 a, 120 b by reducing thepresence of charge trapping defects. With less electron loss at grainand at surface interfaces, photo-conversion efficiency can increase.

As shown in FIG. 2B, after the CdCl₂ activation treatment, thesacrificial layer 118 may be completely fluxed into adjacent firstabsorber layer 120 a and second absorber layer 120 b to the extent thatabsorber layers 120 a and 120 b become one continuous absorber layer 220containing sulfur. However, depending on the thickness of sacrificiallayer 118 deposited on the absorber layer 120 a and the CdCl₂ treatmentconditions, there may be a thin portion of sacrificial layer 118remaining between the absorber layers 120 a, 120 b after the CdCl₂activation treatment.

It should be understood that thicknesses 116 t, 120 at, 118 t, and 120bt (FIG. 1) can each be varied to obtain a desired final thickness ofcontinuous absorber layer 220 and window layer 116. It should also beunderstood that these layer thicknesses may also be varied based on thechosen CdCl₂ activation treatment parameters to obtain a singlecontinuous absorber layer 220. For example, after a desired finalcontinuous absorber layer 220 thickness and material is chosen, theCdCl₂ activation treatment conditions may then be determined to optimizethe grain growth and defect repair of the absorber layers 120 a and 120b (FIG. 1) in a manner that will form continuous absorber layer 220.

The CdCl₂ activation treatment conditions when using sacrificial layer118 are not as restrictive as when forming a conventional PV devicewithout sacrificial layer 118. A thicker sacrificial layer 118 may berequired for higher CdCl₂ concentrations, longer annealing times, andhigher temperatures. The distance of the sacrificial layer 118 from thesurface of absorber layer 120 b which receives the CdCl₂ treatment isdetermined by second absorber layer 120 b thickness 120bt and can bevaried independently of the sacrificial layer thickness 118 t based onthe CdCl₂ activation treatment conditions. For example, 120bt can bevaried based on a chosen final continuous absorber layer 220 thicknessby varying the relative thicknesses 120 at, 120 bt of absorber layers120 a, 120 b, respectively. Choosing a thinner thickness 120 bt wouldplace the sacrificial layer 118 closer to the source of CdCl₂ and heatapplication causing the sulfur material in sacrificial layer 118 to fluxat a higher rate as compared to using a thicker thickness 120 bt.

An example of a more aggressive activation treatment, which may berealized by use of sacrificial layer 118, is provided in the followingexample. CdCl₂ is applied (FIG. 2) over the absorber layer 120 b as anaqueous solution having a concentration of about 100-600 g/L, which canbe 2-4 times more concentrated than in a conventional CdCl₂ activation.Other forms of CdCl₂ treatment may also be used, such as CdCl₂ vapor atambient pressures. Further, the anneal temperature can be up to about700° C., which is 280-300 degrees hotter than typically used.

The CdCl₂ activation treatment may include a single pass or a multiplepass anneal, meaning more than one heating step. One example of amultiple pass anneal employs a first heating of the CdCl₂ treatedabsorber layers 120 a, 120 b to about 450° C. for about 15 minutes and asecond heating to about 450° C. for about 15 minutes. A second exampleof a multiple pass anneal employs a first heating to about 450° C. forabout 15 minutes and a second heating to about 430° C. for about 20minutes. A third example of a multiple pass anneal employs a firstheating to about 430° C. for about 30 minutes and a second heating toabout 430° C. for about 30 minutes. It is possible that, during or priorto the second heating steps just described, additional CdCl₂ can beapplied to the absorber layers 120 a, 120 b, if desired.

During the CdCl₂ treatment, PV device 100 can be annealed at atemperature above about 200° C., for example, in a range of about 200°C. to about 700° C., about 300° C. to about 600° C., about 350° C. toabout 500° C., about 400° C. to about 450° C., about 420° C. to about450° C.

The annealing can be continued for as long as is needed to cause thesacrificial layer 118 to be partially or completely fluxed into adjacentabsorber layers 120 a, 120 b resulting in the formation of continuous ormostly continuous absorber layer 220. A mostly continuous absorber layer220 may result, for example, if not all of sacrificial layer 118 isfluxed into absorber layers 120 a, 120 b. PV device 100 can be heatedfor more than about 10 seconds, for example, in a range of about 10seconds to about 2 hours, about 10 minutes to about 60 minutes, or about15 minutes to about 30 minutes. The anneal times and temperatures ofeach or either of the annealing conditions can be adjusted independentlyor together to achieve continuous absorber layer 220.

FIGS. 3A and 3B respectively show scanning electron microscope images ofa cross section of a conventional PV device 350 formed without asacrificial layer 118 (FIG. 3A) and PV device 100 formed with asacrificial layer 118 (FIG. 3B) which have had a CdCl₂ annealingtreatment under the same conditions. The PV device 350 was initiallyformed with a 450 Å CdS window layer 316 thickness and a 33,000 Å CdTeabsorber layer 320 thickness. The PV device 100 was formed with a 450 ÅCdS window layer 116, a 33,000 Å CdTe first absorber layer, a 450 Å CdSsacrificial layer 118, and a 33,000 Å CdTe second absorber layer. Bothdevices 350 and 100 underwent the same CdCl₂ activation treatment. A 200g/l CdCl₂ solution was sprayed and spun on to each of PV devices 350 and100 and both devices were heated to 430° C. for 20 minutes. The CdCl₂solution was applied a second time and the PV devices 350 and 100 wereheated for a second time to 430° C. for 20 minutes. As shown in FIG. 3A,the CdCl₂ activation treatment led to the formation of gaps 315 in thesemiconductor window layer 316. The gaps 315 result in the shorting ofthe semiconductor absorber layer 320 to the TCO layer 314 contributingto the degradation of the absorber/window p-n junction. Now referring toFIG. 3B, PV device 100 shows a mostly continuous absorber layer 220 withsome residual portions of sacrificial layer 118 not fully dissolved intoabsorber layer 220. FIG. 3B also shows PV device 100 with an improvementin window layer 116 continuity as compared to the gaps 315 in the windowlayer 316 of the PV device 350 of FIG. 3A.

Referring to FIG. 4, after the CdCl₂ activation treatment (FIGS. 2 and3), a back contact layer 124 may be formed over the continuous or mostlycontinuous absorber layer 220. The back contact layer 124 does not havea transparency requirement and thus may be made of a metal such as Mo,Al, Cu, Ag, Au, or a combination thereof. After the formation of theback contact layer 124, a polymer interlayer 126 may be formed beforeaffixing a back cover 128 to form a completed PV device 150. Theinterlayer 126 may be provided over the back contact layer 124 and sidesof the layers (114, 116, 220, and 124) of the PV device 150 of FIG. 1 orPV device 100 of FIG. 4. It is used to supplement bonding between thedifferent layers of the device 150 and to inhibit ingress of water orother contaminants into the device. It may be made of a polymer such asethylene-vinyl acetate.

PV devices formed with sacrificial layers 118 have been found to have ahigher photo-conversion efficiency than PV devices formed withoutsacrificial layers 118 due to the increased continuity of the p-njunction, the more aggressive CdCl₂ activation treatment conditions, andthe addition of sulfur into the absorber layer 220 to passivate defects.The presence of sulfur in a CdTe absorber layer produces an absorberlayer 220 having a CdS_(x)Te_(1-x) structure, at least at areas ofabsorber layers 120 a, 120 b which were most adjacent sacrificial layer118, where CdS_(x)Te_(1-x) is an alloy of cadmium (Cd), sulfur (S), andtellurium (Te), and where x is greater than zero and less than one andrepresents the atomic ratio of sulfur to tellurium in the alloymaterial.

The embodiments described above are offered by way of illustration andexample. Each layer in PV device 100 or 150 may, in turn, include morethan one layer or film. Additionally, each layer can cover all or aportion of the device 100 or 150 and/or all or a portion of the layer orsubstrate underlying the layer. For example, a “layer” can include anyamount of any material that contacts all or a portion of a surface.

It should be understood that the examples provided above may be alteredin certain respects and still remain within the scope of the claims. Itshould be appreciated that, while the invention has been described withreference to the above preferred embodiments, other embodiments arewithin the scope of the claims.

What is claimed as new and desired to be protected by Letters Patent of the United States is:
 1. A photovoltaic device comprising: a first and a second electrode; a window layer containing sulfur in electrical association with the first electrode; and an absorber layer adjacent to the window layer and containing sulfur, at least a portion of which is from a sulfur containing layer other than the window layer, the absorber layer being in electrical association with the second electrode.
 2. The photovoltaic device of claim 1, wherein the sulfur containing layer other than the window layer is a sacrificial layer.
 3. The photovoltaic device of claim 2, wherein the sacrificial layer is arranged between a first and a second portion of the absorber layer before an activation treatment and the portion of the sulfur in the absorber layer from the sacrificial layer is contained within the absorber layer after the activation treatment.
 4. The photovoltaic device of claim 3, wherein at least a portion of the first and second portions of the absorber layer are in contact with each other after the activation treatment.
 5. The photovoltaic device of claim 2 wherein a portion of the sacrificial layer remains present as a distinct layer in the absorber layer.
 6. The photovoltaic device of claim 2, wherein the window layer and the sacrificial layer are formed of the same sulfur containing material.
 7. The photovoltaic device of claim 1, wherein the window layer comprises a material selected from the group consisting of cadmium sulfide and cadmium zinc sulfide.
 8. The photovoltaic device of claim 7, wherein the sacrificial layer comprises a material selected from the group consisting of cadmium sulfide and cadmium zinc sulfide.
 9. The photovoltaic device of claim 7, wherein the absorber layer comprises cadmium telluride.
 10. A method of manufacturing a photovoltaic device, the method comprising: forming a first electrode; forming a window layer containing sulfur in electrical association with the first electrode; forming a first absorber layer adjacent the window layer; forming a sacrificial layer containing sulfur adjacent the first absorber layer; forming a second absorber layer adjacent the sacrificial layer; heating the device layers such that at least a portion of the sulfur from the sacrificial layer fluxes into the first and second absorber layers; and, forming a second electrode in electrical association with the second absorber layer.
 11. The method of claim 10, further comprising treating at least the second absorber layer with a compound comprising chlorine in association with the heating.
 12. The method of claim 10 wherein the fluxing of the sacrificial layer into the absorber layers decreases a fluxing of the sulfur from the window layer into the first absorber layer during the heating.
 13. The method of claim 10, wherein the sacrificial layer is formed in contact with the first absorber layer and the second absorber layer.
 14. The method of claim 10, wherein the window layer and the sacrificial layer are formed of the same material.
 15. The method of claim 10, wherein the window layer comprises a material selected from the group consisting of cadmium sulfide and cadmium zinc sulfide.
 16. The method of claim 15, wherein the sacrificial layer comprises a material selected from the group consisting of cadmium sulfide and cadmium zinc sulfide.
 17. The method of claim 10, wherein the first and second absorber layers each comprise cadmium telluride.
 18. The method of claim 11, wherein the sacrificial layer and the first and second absorber layers are formed to thicknesses such that after the treating and heating steps at least a portion of the first and second absorber layers are in contact with each other.
 19. The method of claim 11, wherein the sacrificial layer and first and second absorber layers are formed to thicknesses such that after the treating and heating steps a portion of each of the first and second absorber layers are separated by a portion of the sacrificial layer.
 20. The method of claim 10, wherein the sacrificial layer is formed to a thickness of between about 50 Å and about 1000 Å.
 21. The method of claim 20, wherein the first absorber layer is formed to a thickness of between about 10 Å and about 50,000 Å.
 22. The method of claim 20, wherein the second absorber layer is formed to a thickness of between about 500 Å and about 50,000 Å.
 23. The method of claim 20, wherein the window layer is formed to a thickness of between about 50 Å and about 2,000 Å.
 24. The method of claim 20, wherein the sacrificial layer is formed to a thickness of between about 100 Å and about 800 Å.
 25. The method of claim 24, wherein the first absorber layer is formed to a thickness of between about 10,000 Å and about 30,000 Å.
 26. The method of claim 24, wherein the second absorber layer is formed to a thickness of between about 10,000 Å and about 40,000 Å.
 27. The method of claim 24, wherein the window layer is formed to a thickness of between about 75 Å and about 1000 Å.
 28. The method of claim 10, wherein heating the device layers comprises heating the device to between about 300° C. and about 600° C.
 29. The method of claim 28, wherein heating the device layers comprises heating the device to between about 400° C. and about 450° C.
 30. The method of claim 11 wherein the compound comprising chlorine comprises a material selected from the group consisting of CdCl₂, NH₂Cl, ZnCl₂, and TeCl₄.
 31. The method of claim 11, wherein the compound comprising chlorine comprises an aqueous CdCl₂ solution having a concentration between about 100 g/L and about 600 g/L.
 32. The method of claim 30 wherein, wherein heating the device layers comprises a first heating at a first temperature and a second heating at a second temperature.
 33. The method of claim 32, wherein the first and second temperatures are different.
 34. The method of claim 30, wherein the treating step comprises more than one treatment step with the compound comprising chlorine.
 35. The method of claim 34, wherein the heating steps comprise a first heating to between about 400° C. and about 600° C. for between about 10 seconds and about 2 hours after a first compound comprising chlorine treatment and a second heating to between about 400° C. and about 600° C. for between about 10 seconds and about 2 hours after a second compound comprising chlorine treatment step.
 36. The method of claim 35, wherein the first and second heating steps are each to between about 420° C. and about 450° C. for between about 15 minutes and about 30 minutes. 